[PATCH v2] common: fdt: Remove additional 4k space for fdt allocation

[Stephen Warren]

On 6/11/20 5:10 AM, Michal Simek wrote:
> From: Ashok Reddy Soma <ashok.reddy.soma at xilinx.com>
> 
> There is no technical reason to add additional 4k space for FDT. This space
> is completely unused and just increase memory requirements. This is
> problematic on systems with limited memory resources as Xilinx Zynq
> CSE/ZynqMP mini and Versal mini configurations.

I haven't looked into whether it's useful to reserve extra space yet.
But I have to say I find it extremely unlikely that 4K space usage is
problematic for a system large enough to run U-Boot, unless this is part
of a much larger push to trim memory usage.

> The patch is removing additional 4k space and also increasing alignment to
> 64 to be aligned with 64bit systems.

> diff --git a/common/board_f.c b/common/board_f.c

> -		gd->fdt_size = ALIGN(fdt_totalsize(gd->fdt_blob) + 0x1000, 32);
> +		gd->fdt_size = ALIGN(fdt_totalsize(gd->fdt_blob), 64);

So IIRC the alignment parameter is bytes not bits. I don't follow why a
64-bit system would need 64-byte alignment? IIRC, the stack alignment
requirement is only 16 bytes, so the presumably isn't what this change
is trying to fix.

I'd suggest making the alignment-change and extra-size-removal patches
separate patches so that any issues caused by the change can easily be
tracked to one of the separate logical changes by git bisect etc.